Chloride-related current fluctuation in amphibian skin

Fluctuation in transepithelial current was analysed in skins of Rana esculenta and Bufo viridis. Perturbation of the tissues to serosa + 40 mV or + 80 mV activated a pathway for conductive Cl transport and led to the appearance of a Lorentzian component in the power density spectrum. The presence of Cl on the mucosal side was mandatory for the observation of Lorentzians. Corner frequencies, f_c, ranged between 48 Hz and 102 Hz. The mean value was slightly larger at 40 mV than at 80 mV (88.3±4.4 versus 72.5±6.4 Hz). Plateau values, S_o, were proportional to the magnitude of the activated Cl current. Single-channel currents of 48.3 ±5.2 fA and 93.0±8.7 fA were calculated at 40 mV and 80 mV, respectively, with the assumption of equal open and closed probabilities of the channels. From these data, a voltage-independent open-channel conductance of about 1.2 pS is obtained. Activation of Cl conductance was associated with an increase in channel density. Stimulation of Cl conductance by procaine did not affect S_o and f_c despite considerable stimulation of transepithelial Cl current. This could indicate that non-gated channels participate in the voltage-sensitive Cl conductance. Mucosal application of inhibitors of Cl conductance (3,5-dichlorodiphenylaminocarboxy acid, MK-196) decreased S_o in a concentration-dependent manner, but had no effect on f_c. The data could support the hypothesis that the voltage-sensitive transepithelial Cl transport is localized to a cellular compartment, which is most likely the mitochondria-rich cells. The possibility cannot be excluded, on the other hand, that the fluctuation in current originates from highly organized, specific sites in the junctional complexes.